Heat and pressure element for weld



Dec. 22, 1953 E. v. DETTMER v 2,663,350

HEAT AND PRESSURE ELEMENT FOR WELDING THERMOPLASTIC FILMS Filed Jan. 2, 1952 17 7 11 zz 11 y y f ,y 10A i im d; R tigui lo 7 12 2X Z @fr INVENTOR Ea/Wara/ K Dell/mer BY A l y ATTORNEYS.

Patented Dec. 22, .1953

UNirso :STAT-Es PATENT OFFICEl HEAT AND PRESSURE ELEMENTFOR WELD- ING THERMOPLASTIC FILMS Edward V. Dettmer, Bay City, Mich., assgnor to The `Dowllh'einical Company, Midland, Mich., a, corporation of Delaware .Application..lanuary 2, 1952,` Serial No. 264,61

3`Claims. (Cl. 1545-1) smooth metal belts, runder pressure, and yconveying the filmspastgheatingelements The machine of .the latter patent opera-tes intermittently, the iilms being -inteped between Lcloth or wire mesh belts and sheatibeing ,applied through the belts by hot jaws Flor reasons :to be stated, it isidesired/to provide'a,1heating element, for use in contact with the lms, which avoids some of the principal' diii'icnlties .heretofore encountered. It is desirable to avoidethe .use'yofhot, highly polished metal surfaces in the sealing operation, as the fused plastic is too prone Vto adhere to such surfaces. Rougher--surf-acestendto avoid adherence tothe lm,butthose -used heretofore leave the sealedarea-witha seuied or -abraded surface, if :the nlmr'is drawn-past-suchasurfaee while still het. Machines of the types mentioned are not adapted to sealing the folded end flaps across the flat faces of packages such as cereal boxes or the more yieldable packages such as wrapped bread, since, in such operations, heat can be applied from but one side of the overlapped iilm. It is the object of this invention to provide a lm welding element whose use will avoid the above mentioned difficulties.

According to the present invention, the said desired results are obtained through the provision and use of a particular type of film-contacting surface on the heating element used for welding thermoplastic iilms. The face of such an element `in contact with the iilm to be welded is composed of wire mesh of such construction that most, and preferably all, of the wires contacting the film are parallel to one another and are preferably aligned in the direction of movement of theiilm through the machine. The heating element is provided with an internal reservoir of oily lubricant, and with channels through which said lubricant is fed to the wire mesh surface at a rate suiiicient to maintain at that surface a liquid iilm of the lubricant. As a result, the lm does not stick to the surface, even though the vlatter feels smooth, and is not scuied or 2 i abraded by -that surface,.even though Ait appears to be somewhat rough due to its woven condition. When heat is applied to the iilm (under pressure, where practical), and the 'lm is then released, a good, smooth weld is obtained.

The invention will be described more Yin detail with reference to the. accompanying drawing wherein: Y

Fig. 1 is a longitudinal section through one form of a pair of the heat and pressure members of the invention, with a pair of ilms to be welded shown as interposed between the ypair Vof welding elements; A

Fig. 2 is an end view of ione of the heating elements of Fig. l;

Fig. 3 is a cross-section of one of the heating elements, taken along line 3-3 of Fig. 1;

Fig. 4 is a plan view of one type of woven wire screen suitable for use asthe working face of the heating element; and,

Fig. 5 is a longitudinal sectionA through such screen, taken along line v5--5 of Fig. 4. Through-V out the drawing, the Vspacing of the various members of the assembly isexaggerated, for clarity.

rlhe heating elements of the invention com'- prise a dense metal Abody member I0, of high thermal capacity, longitudinally drilled to provice sockets il for insertion of electric resistance heaters, the lead wires l2 of which are shown in rgs. 1 and 2. Body It is provided with rearwardly extending brackets i3. A plurality of fine channels ld is provided through body I6 for passage of lubricant from the rear to the face of that body. One or a plurality of sheets of fabric i, or other wicking material, is positioned to the rear of body member IU, and is held in place by cover plate I6 which, in turn, is positioned within brackets i3 and may be pressed firmly enough against the lubricant containing wicking i5 by means of pressure screws Il, to maintain a film of oil on screen i9. The lubricant content ci" the confined wicking i5 can be maintained or replenished through ports I8 provided in cover plates l. There is stretched across the face of body member l a woven Wire screen I9 in which the only elements lying in the exposed plane are parallel to one another, and are preferably the warp members Ei) of screen I9 or of a corduroy Woven screen with no exposed cross members. It is preferred that screen I9 be disposed with the Warp members 29 lying in the direction of movement of film 2l past the welding elements. At the points where the weft or cross-members 22 of screen I9 cross the warp members 2i! and are visible on the exposed face of screen I9, the warp members 2D are so crimped that the weft strands lie slightly below the plane of that exposed working face, and this relationship is shown most clearly in Fig. 5.

The heating elements of the present invention may be employed in any of several assemblies already known to be useful in welding plastic lms. In operation, the heat and pressure members are heated to the required temperature, and sufficient pressure is applied to the lubricant saturated wicking to supply a liquid lm of lubricant to the exposed face of the wire mesh. Two or more thicknesses of plastic lm to be welded are moved into position between a pair of the heating elements, and the latter are held in contact with the lms, under positive pressure, long enough to fuse and weld the films together. The operation may be intermittent, if

desired, with the heaters moving together and' apart at regular intervals as the films are introduced tothe welding zone and become welded. Continuous operation, with the heaters in xed position, is also possible. In the latter case, a nlm-wrapped package, or other item requiring a lm to lrn seal, is drawn past one, or between two of the heaters and is moved at a rate which will permit the formation of a Weld before the article loses contact with the heater. In either case, there is no tendency for the film to stick to the hot welding element, and no scuing of the hot film.

The metallic elements of the invention may be made of any metal with high heat capacity. Thus, copper or a copper alloy is the preferred material for the body member I0 and for the screen facing I9, though the latter may be made of any metal which is not catalytically destructive of the lm at the temperature employed, and the former, being out of contact with the nlm, is not so limited.

Numerous plastic films are known which can be welded advantageously with the herein-described apparatus. These include, but are not limited to, vinylidene chloride copolymer films, vinyl chloride-vinyl acetate copolymer lms, and rubber hydrochloride films.

I claim:

l. In an apparatus for heat welding plural 4 thicknesses of organic thermoplastic film, a heating element comprising a metallic body of high heat capacity; means for heating said body to a film welding temperature; a Woven wire screen attached to and constituting the working face of said body, the warp wires of which constitute most of the exposed surface of the screen; channels through said bodyV communicating with said screen; and means for supplying a liquid lubricant through said channels to the screen.

2. In an apparatus for heat welding plural thicknesses of organic thermoplastic film, a heating element comprising a metallic body of high heat capacity; means for heating said body to a lm Welding temperature; a woven wire screen attached to and constituting the working face of said body, the warp members of said screen lying parallel'to the direction of travel of film through the apparatus and constituting the exposed surface of the screen, and being the only wires to contact films during a welding operation; channels through said body communicating with said screen; and means for supplying a liquid lubricant through said channels to the screen.

3. In an apparatus for heat welding plural thicknesses of organic thermoplastic film, a heating element comprising a metallic body of high heat capacity; means for heating said body to a nlm welding temperature; a woven wire screen attached to and constituting the working face of said body, the Vwarp wires of which constitute most of the exposed surface of the screen; channels through said body communicating with Said screen; oil-absorptive wicking disposed rearwardly of said body in communication with said channels; means for supplying oil to the wicking; and, means for expressing oil ata controlled rate from the wicking to maintain a lm of oil on the screen during operation of the apparatus.

' EDWARD V. DETTMIER.

References Cited in the le of this patent UNITED STATES PATENTS 

